The Op has stated that he does not have the Finances, or the Inclination to replace the "Old" Gas unless it is Absolutely necessary. The only way to determine if the gas in his tank is Good or "Bad" is to test it.
Consider the following statements....
ALL Gas, less than One year old, no mater how it is stored, is Good.
ALL Gas, over Two years old, no mater how it is stored, is Bad.
If you conclude that both statements are False; The conclusion is that ...
Gas less than one year Old May be Bad. and ... Gas over Two years Old May be Good.
In other words, The age of the Gas has little bearing on its viability and Gas of any age May be Good Or Bad. Who knows?
One thing that is lacking in the whole debate, is the definition of "Bad."
Some people have stated that any gas older than 30 days is Bad. Based on what?
Without a definition of Good or Bad there is no basis of discussion.
I have proposed that Gas that is clear and will not hold a "Foam Head" for more than 5 seconds is Good.
It is a simple test that anyone with minimal skills can perform any zero cost. What more can you ask?
The alternative is to dispose of whatever quantity of gas you may have, that is more than a few weeks old,
on the off chance that it may destroy your engine if you were to use it.
I am willing to entertain any other definition of Good/Bad, along with a way of determining that same condition, that anyone wished to supply.